Turbulence characteristics of surface boundary layer over the Kalpakkam tropical coastal station, India

Abstract

In this study turbulent fluxes and their intensity features are studied in different seasons at the tropical Indian coastal station, Kalpakkam. Measurements from Ultrasonic anemometer at 10 m agl over 30-day period of four seasons (winter 1–30 January; summer/spring 1–30 April; SW monsoon 1–30 July; NE monsoon 1–30 October) in 2013 and 2014 are used for this work. Various surface layer parameters viz, friction velocity (u*), Obukhov length (L), momentum flux (M), turbulent heat flux (H), turbulence kinetic energy (TKE) are computed using eddy correlation method. Results indicate that the study region is highly turbulent in summer followed by NE monsoon, winter and SW monsoon seasons. Derived parameters indicate that shear is the main contributing mechanism for TKE generation during SW monsoon and both shear and buoyancy contributed for the generation of TKE in other seasons. Site specific turbulent intensity relationships were developed by analyzing second order moments of 3D wind components as a function of stability parameter (z/L). The turbulent components of wind followed 1/3 power law in the unstable regime and − 1 power law in the stable regime. Comparisons with previous studies indicate that the turbulent intensity for horizontal winds at the coastal station is relatively less especially in the unstable conditions. The derived relationships are found to be unique and vary seasonally and suggest their application for improved modeling of atmospheric dispersion in the study domain. Rate of dissipation of TKE (ϕe) for stable and unstable conditions at the observation site is different from the earlier proposed relationships in the literature. Thus, a new relationship is proposed for the better fit of the data at this site.